The world of sports routinely kicks up stories so improbable and dramatic that Hollywood could never concoct them, so it’s no wonder they’re catnip for the movie business. Strangely enough, though, no one ever made a film about the life of James J. Braddock, a light-heavyweight prizefighter whose boxing career took a sharp downturn right before the Great Depression. Having lost all his earnings in the stock market crash, Braddock was reduced to working part-time as a longshoreman and standing in bread lines, before a miraculous comeback in 1935 that led to his winning the heavyweight championship of the world. The legendary sportswriter Damon Runyon dubbed Braddock “Cinderella Man,” which is the title of Ron Howard’s biopic starring Russell Crowe.Crowe gave one of his least interesting performances of his career for Howard in 2001’s A Beautiful Mind. He’s much better here, especially in the scenes when Braddock struggles to keep his head up while he’s sliding down. You can feel the desperate-loser vibe leaking from him when he pleads with a boxing commissioner (Bruce McGill) to keep him on the rolls as a fighter, and later when he returns to Madison Square Garden to beg for spare change from the sportswriters who once covered him. He has a marvelous bantering rapport with Paul Giamatti, who’s full of period flavor as Braddock’s indefatigable manager Joe Gould. Crowe flashes that demonic grin of his during the climactic fight with heavyweight champ Max Baer (played as a preening trash-talker by Craig Bierko), as if to say, “That all you got?”It’s good that Crowe’s in top form once again, because the only thing that keeps Cinderella Man tolerable is the quality of its acting. (Sadly, this does not include Renée Zellweger, who gives a one-note performance in the unrewarding part of Braddock’s supportive wife Mae.) Howard can’t blow any dust off the hoary conventions of sports flicks, and he suffocates the film in good taste and a Sunday-school tone. It’s part of a depressing trend in sports movies: This one, Ali, Seabiscuit, and to a lesser extent Miracle all present themselves as The Story of America. Sports are dramatic enough in themselves — why do they need this treatment? The windiness and pretension in Cinderella Man are enough to send you scurrying into a theater showing The Longest Yard.Then again, you’d be better off going to Lords of Dogtown, which is also based on a true story. Skateboarding culture ostensibly took root in the mid 1970s in Dogtown, the name for the economically depressed area of Southern California that includes Venice, Ocean Park, and the southern half of Santa Monica. There, a group of surfers called the Z-Boys took advantage of technological innovations that let skaters perform surfing moves on skateboards. Kept in line by surf-shop owner/mentor Skip Engblom, the group (whose ethnic diversity reflected the area’s white, Latino, and Japanese-American makeup) was defined by the personalities of Tony Alva, the daredevil with a rock star’s magnetism; Jay Adams, the brilliant, self-destructive clown prince; and Stacy Peralta, the most business-savvy of the skaters. The Z-Boys, who probably would have dead-ended otherwise, took what had been an outdated fad and made it into an outlet for creative expression and eventually into the multi-million-dollar subculture it is today.Their story was already told in Peralta’s excellent 2002 documentary Dogtown and Z-Boys. Now Peralta has written the script for a Hollywood biopic that serves as a good companion piece. The director is Catherine Hardwicke, who showed a terrific feel for the unfashionable SoCal atmosphere in her 2003 debut film, Thirteen. This movie benefits from the same quality and from the fact that it isn’t nearly as histrionic. There are some unnecessarily slow spots here, as well as a fabricated romantic subplot that the script didn’t need, but the movie’s low-key kitchen-sink realism is the best possible medium for the story.A largely unknown cast fleshes out most of the roles. Victor Rasuk, an untrained actor whose one previous credit was the awkward-teen lead role in Raising Victor Vargas, plays Alva and wears the air of a self-assured whiz kid quite well. Emile Hirsch, an actor who never made much of an impression in any of his previous roles, uncorks himself to great effect as Adams, most memorably when he does a spastic dance for the benefit of Alva’s sister (Thirteen co-star Nikki Reed). Best of all is Heath Ledger as Engblom. He’s been stuck playing noble, upright stiffs in movies like The Four Feathers and Ned Kelly, but playing a surfer dude suits him much better. His weird, tic-laden performance is very funny, and he also captures Engblom’s mixed feelings as he watches helplessly while the kids he once bossed around become too big for him. Lords of Dogtown tracks the Z-Boys’ lives and shows how the skaters, at times unwillingly, grow up, and this gives the film a resonance that Cinderella Man’s old-school hokum can’t possibly match.